I second this from experience.
My '82 v8 280zx has been in the bodyshop for 2 years now coming this June. I don't understand why. They're charging me full price, but I think it's all the custom work I'm having them do (ie not just molding a body kit and painting the car). Although I miss the hell out of that car, I see it as free storage while I can finish my other projects.
My '83 280zxt - I've given to a painter through a friend of a friend that I was supposed to do bartering work for. I held up on my end, but then he fell through, so he passed the burden to the guy that has the car right now. I gave it to him with most body work completed and the car stripped down - just needed it painted. It's been 7-8 months.
My '77 280z 2+2 - When I lived in Victoria a few years ago, one of the body guys at the dealership I worked at was also a Z guy, and work was slow so he offered to paint my car for cheap. Any time there's any work done to it, it's because I drove 3 hours away from here to work on it myself. He's had it for close to 5 years now.
I'm going to be paying an arm and a leg for the bodywork on my widebody project, so hopefully that won't drag on. Plus, I set out a payment system with the body guy. I will pay him on monthly increments as long as I'm seeing a decent amount of progress. For example, $1000 down, and then increments of $1250 as he works on it. Maybe that could be an idea for you?